1. Field of the Invention
The present invention relates to an illuminating optical device used for photographing an eye fundus.
2. Related Background Art
A prior art illuminating optical device is built in an eye photographing apparatus, for example, and utilized to illuminate an eye fundus. When the eye fundus is photographed, light reflected by the eye fundus is directed to an imaging plane. Since the reflective index of a cornea is usually larger than that of the eye fundus, the eye to be checked is illuminated in a ring shape as shown in Japanese Patent Publication No. 53-43277 in order to suppress the reflection by the cornea and a light beam reflected by the eye fundus is taken out of a center area which is separate from the ring-shaped illumination area. This is the so-called ring shape illumination method. A stroboscope light source such as, a discharge tube is used to instantly irradiate with a strong illumination light the eye fundus.
However, in the prior art, only one or two, at most, forward light beams of the light beams emitted in every direction from the light emitting device such as the stroboscope light source are utilized and the light beams emitted in other directions do not contribute to the illumination of the eye fundus. As a result, in photographing the eye fundus, the photographed image may be not clear because of insufficient light. However, because the power supplied to the stroboscope light source is limited, an illumination light of a larger intensity is demanded.